Automated X-ray Inspection (AXI) is an important technique utilized by electronics manufacturers to “see” through obstructions on crowded printed circuit boards to detect manufacturing defects such as hidden solder-related problems. One machine employed in AXI is Agilent's 5DX automated X-ray test system, which is capable of detecting more than 97 percent of all solder related defects (such as opens, shorts, voids, and insufficient or excess solder) and over 90 percent of all manufacturing defects on printed circuit board assemblies (PCBAs). Automated X-ray Inspection is typically employed in combination with other test solutions such as automated optical inspection (AOI) and in-circuit test (ICT).
X-ray testing is probably the best technology for efficiently and accurately inspecting ball grid array (BGA), ceramic column grid array (CCGA), chip scale package (CSP) and other area array solder joints. The Agilent 5DX AXI machine can zero-in on specific layers of a PCBA to inspect surface features with a high degree of accuracy, and is capable of seeing through obstructions such as BGA packages, RF shields and component packages to inspect hidden solder joints on both sides of a PCBA. The Agilent 5DX AXI machine also inspects traditional SMT and through-hole components such as QFPs, SSOPs, connectors, and chip components.
In addition to capturing X-ray images, the Agilent 5DX AXI machine transforms captured images into useful “actionable” information by means of a suite of algorithms that isolate open solder joints, solder bridges, misaligned and missing components, insufficient and excess solder, and solder voids. Defect data, including component, pin number, defect type, and X-ray image, are reported to an Agilent Repair Tool (ART) for repair.
The Agilent 5DX AXI machine includes a suite of tools that simplify most day-to-day development tasks in X-ray test. CAD files are translated automatically. Program thresholds are tuned by the system to increase call accuracy. A program advisor checks tests and provides recommendations to improve accuracy and fault coverage. Defect coverage reports inform the user about coverage being obtained and indicate where coverage may be improved.
As illustrated in FIG. 1, one version of a prior art Agilent 5DX automated X-ray inspection machine 100 comprises main cabinet 120, X-ray tube tower 130, rear electronics cabinet 140, monitor/keyboard cart 150, computer monitor 160 and computer keyboard 170. Keyboard 170, monitor 160 and a computer workstation (not shown in the FIGS.) serve as the user interface to X-ray inspection machine 100. X-ray tube tower 130 contains and provides access to X-ray tube 200 (not shown in FIG. 1, but shown in FIG. 2).
FIG. 2 shows a schematic cross-section of prior art X-ray tube 200 from Agilent 5DX automated X-ray inspection machine 100. As illustrated in FIG. 2, X-ray tube 200 comprises electron gun assembly 210, electron beam accelerator 220 having upper portion 230 and lower portion 240. Electron gun assembly 210 is attached to upper portion 230. X-ray beam drift assembly 225 is connected to lower portion 240 of electron beam accelerator 220. X-Ray target 235 is located beneath and attached to X-ray beam drift assembly 225. Electromagnets (not shown in the drawing) are disposed around X-ray beam drift assembly 225 and deflect electrons projected through assembly 225 onto appropriate portions of target 235.
As shown in greater detail in FIG. 3, electron beam accelerator 220 comprises a plurality of stages 250, 260, 270 and 280 that are stacked one atop the other and interconnected by means of KOVAR collars 252, 254, 256 and 258 interposed between adjoining stages. Each of stages 250, 260, 270 and 280 is designed and formed to permit a 30 keV to 60 keV voltage gradient to be developed thereacross. Each of stages 250, 260, 270 and 280 comprises, respectively, glass body 292, 294, 296 or 298. Each of glass bodies 292, 294, 296 and 298 has, respectively, central aperture 293, 295, 297 or 299 disposed therethrough, each such central aperture defining inner surface 301, 309, 305 or 307.
Continuing to refer to FIG. 3, stainless steel electron beam guides 312, 314, 316 and 318 are positioned within central apertures 293, 295, 297 and 299. Outer surfaces 302, 304, 306 and 308 of stainless steel electron beam guides 312, 314, 316 and 318 are connected to inner portions 251, 253, 255 and 257, respectively, of KOVAR collars 252, 254, 256 and 258.
As will be seen by referring to FIGS. 2 and 3, KOVAR collars 252, 254, 256 and 258 and stainless steel beam guides 312, 314, 316 and 318 have rather elaborate and complicated forms and shapes, which those skilled in the art will understand increase considerably the cost of manufacturing and assembling electron beam accelerator 220. The shapes, forms and compositions of such collars and beam guides are necessary owing to the extreme thermal and mechanical stresses to which electron beam accelerator 200 are subjected during use. Such shapes, forms and compositions arise from the disparity in physical properties between glass bodies 292, 294, 296 and 298, on the one hand, and metal collars 252, 254, 256 and 258 and beam guides 312, 314, 316 and 318, on the other hand, as well as the requirements for mechanical strength in the column formed by stacked bodies 292, 294, 296 and 298 of electron beam accelerator 220.
It will now be seen that forming the complicated shapes and forms of, and employing the expensive materials used to manufacture, glass bodies 292, 294, 296 and 298, metal collars 252, 254, 256 and 258 and stainless steel beam guides 312, 314, 316 and 318 increase manufacturing costs of accelerator 220. What is needed is a simpler means of attaching adjoining stages to one another, in combination with lower-cost materials and structures for forming beam guides.